Water-soluble films are gaining wider acceptance for use as packaging materials. Packaging materials include films, sheets, blown or molded hollow bodies (i.e. sachets, pouches, and tablets), bottles, receptacles and the like. Often water-soluble films, when used in the preparation of certain types of these articles, such as sachets and pouches, leak and/or become sticky when exposed to small amounts of water contamination or high humidity, which can make them unsuitable for usage in the packaging and preservation of the compositions contained therein.
The most common consumer complaints for water-soluble pouches are linked to unwanted pouch dissolution when accidentally exposed to water, such as when water gets inside the outer packaging in which the pouches are sold and stored after purchase, from wet hands, high humidity, leaking sinks, or pipes during storage, etc. This may cause the water-soluble pouches to leak prior to use and/or stick together. The second most frequent complaint is that of the water-soluble pouch failing to fully dissolve upon use. Thus, there remains an unmet need for water-soluble films and pouches that can resist dissolution and/or leakage after exposure to small amounts of water yet can subsequently dissolve very quickly when immersed in an aqueous solution, such as rinse and/or wash water.
It has been known since the 1960s that certain salts, when added to polyvinyl alcohol (PVOH) solutions, may cause the PVOH to precipitate. These salts are generally seen as being useful for solidifying aqueous PVOH. Another disclosure of the use of salts in water soluble films is in U.S. Pat. No. 5,429,874, VanPutte. The VanPutte patent is directed to a water soluble film suitable for packaging caustic chemicals that has an outer layer of a water soluble polymeric material, and an inner layer of polymeric material which is compatible with the contents of a package made from the film. An intermediate layer can optionally be included to contribute to the tensile strength, bulk, abuse resistance, or some other property of the film. Water soluble fillers such as salt can optionally be added to one or more of the polymeric materials, prior to or during extrusion of the film, to improve the processability of the film or its rate of dissolution in water, or to add a pigment to the film.
It is known that when untreated pouch surfaces are exposed to droplets of water, these untreated pouch surfaces tend to dissolve and/or leak. However, it was surprisingly found that when a Na2SO4 solution is applied to the outside surface of a PVOH pouch, and the outside surface of the pouch is exposed to small amounts of water, the treated pouch does not substantially dissolve and/or leak. Rather, when the treated pouch is exposed to small amounts of water, it exhibits reduced leakage and increased resistance to pouch-to-pouch stickiness.
By adding particular salts to the outside surface of a water-soluble (esp. polyvinyl alcohol) film, resistance to exposure from small amounts water (i.e. wet hands, droplets) can be achieved while not appreciably affecting the water-soluble pouch dissolution profile when the product is immersed in an aqueous solution (e.g. water bath). Incorporating the salt into the outermost part of the water-soluble film can be achieved in a variety of ways that includes conventional powdering, coating, casting, or other methods used in the production of films. The salt concentration may be adjusted to achieve the desired dissolution properties and to optimize pouch aesthetics. The water-soluble film described herein can be used in the production of any pouched product, such as for example, pouches containing: laundry detergent compositions, automatic dishwashing detergent compositions, hard surface cleaners, fabric enhancers and/or fabric softeners, and new product forms where contact with small amounts of water could create premature pouch dissolution, unwanted pouch leakage and/or undesirable pouch-to-pouch stickiness.